Platinum complexes having benzyl-based diphosphine ligands for the catalysis of the alkoxycarbonylation of ethylenically unsaturated compounds

ABSTRACT

Platinum complexes having benzyl-based diphosphine ligands for the catalysis of the alkoxycarbonylation of ethylenically unsaturated compounds.

The present invention relates to platinum complexes having benzyl-baseddiphosphine ligands for the catalysis of the alkoxycarbonylation ofethylenically unsaturated compounds.

The alkoxycarbonylation of ethylenically unsaturated compounds is aprocess of increasing significance. An alkoxycarbonylation is understoodto mean the reaction of ethylenically unsaturated compounds such asolefins with carbon monoxide and alcohols in the presence of a metal ora metal complex and a ligand to give the corresponding esters:

WO 2011/083305 A1 describes a method of alkoxycarbonylation. Thecomplexes described therein, as well as the ligands, have palladium ascentral atom.

A disadvantage of palladium is its high cost.

The technical problem addressed by the present invention is that ofproviding novel complexes having a less costly metal than palladium asthe central atom. The complex is additionally to achieve goodconversions in alkoxycarbonylations.

This object is achieved by a complex according to Claim 1.

Complex comprising Pt and a compound of formula (I)

whereR¹, R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀-aryl,—(C₆-C₂₀-heteroaryl;at least one of the R¹, R², R³, R⁴ radicals is a —(C₆-C₂₀-heteroarylradical having at least six ring atoms;andR¹, R², R³, R⁴, if they are —(C₁-C₁₂-alkyl, —(C₃-C₁₂-cycloalkyl,—(C₃-C₁₂-heterocycloalkyl, —(C₆-C₂₀-aryl or —(C₆-C₂₀-heteroaryl,may each independently be substituted by one or more substituentsselected from: —(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl, —OH, —NH₂, halogen.

The expression (C₁-C₁₂-alkyl encompasses straight-chain and branchedalkyl groups having 1 to 12 carbon atoms. These are preferably(C₁-C₈-alkyl groups, more preferably (C₁-C₆)-alkyl, most preferably(C₁C₄)-alkyl.

The expression (C₃-C₁₂-cycloalkyl encompasses mono-, bi- or tricyclichydrocarbyl groups having 3 to 12 carbon atoms. Preferably, these groupsare (C₆-C₁₂-cycloalkyl.

The expression (C₃-C₁₂)-heterocycloalkyl encompasses nonaromatic,saturated or partly unsaturated cycloaliphatic groups having 3 to 12carbon atoms, where one or more of the ring carbon atoms are replaced byheteroatoms. The —(C₃-C₁₂)-heterocycloalkyl groups have preferably 3 to8, more preferably 5 or 6, ring atoms. In the heterocycloalkyl groups,as opposed to the cycloalkyl groups, one or more of the ring carbonatoms are replaced by heteroatoms or heteroatom-containing groups. Theheteroatoms or the heteroatom-containing groups are preferably selectedfrom O, S, N.

The expression (C₆-C₂₀-aryl encompasses mono- or polycyclic aromatichydrocarbyl radicals having 6 to 20 carbon atoms. These are preferably(C₆-C₁₄)-aryl, more preferably (C₆-C₁₀-aryl.

The expression (C₆-C₂₀)-heteroaryl encompasses mono- or polycyclicaromatic hydrocarbyl radicals having 6 to 20 carbon atoms, where one ormore of the carbon atoms are replaced by heteroatoms. Preferredheteroatoms are N, O and S. The (C₆-C₂₀)-heteroaryl groups have 6 to 20,preferably 6 to 14 and more preferably 6 to 10 ring atoms. Thus, forexample, pyridyl in the context of this invention is a C₆-heteroarylradical; furyl is a C₅-heteroaryl radical.

Suitable (C₆-C₂₀)-heteroaryl groups having at least six ring atoms areespecially pyridyl, pyridazinyl, pyrimidyl, pyrazinyl, benzofuranyl,indolyl, isoindolyl.

The expression halogen especially encompasses fluorine, chlorine,bromine and iodine. Particular preference is given to fluorine andchlorine.

In one embodiment, at least two of the R¹, R², R³, R⁴ radicals are a—(C₆-C₂₀)-heteroaryl radical having at least six ring atoms.

In one embodiment, the R¹ and R³ radicals are each a—(C₆-C₂₀)-heteroaryl radical having at least six ring atoms.

In one embodiment, the R¹ and R³ radicals are each 2-pyridyl.

In one embodiment, R² and R⁴ are —(C₁-C₁₂)-alkyl.

In one embodiment, R² and R⁴ are tert-butyl.

In one embodiment, the compound (I) has the structure (1):

The invention further relates to the use of a complex according to theinvention for catalysis of an alkoxycarbonylation reaction.

Process comprising the process steps of:

a) initially charging an ethylenically unsaturated compound;b) adding an above-described complex, or

-   -   a compound of formula (I)

whereR¹, R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀-aryl,—(C₆-C₂₀)-heteroaryl;at least one of the R¹, R², R³, R⁴ radicals is a —(C₆-C₂₀)-heteroarylradical having at least six ring atoms;andR¹, R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl,—(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl or —(C₆-C₂₀)-heteroaryl,may each independently be substituted by one or more substituentsselected from: —(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl, —OH, —NH₂, halogen,anda substance comprising Pt;c) adding an alcohol;d) feeding in CO;e) heating the reaction mixture from a) to d), with conversion of theethylenically unsaturated compound to an ester.

In this process, process steps a), b), c) and d) can be effected in anydesired sequence. Typically, however, the addition of CO is effectedafter the co-reactants have been initially charged in steps a) to c).Steps d) and e) can be effected simultaneously or successively. Inaddition, CO can also be fed in in two or more steps, in such a waythat, for example, a portion of the CO is first fed in, then the mixtureis heated, and then a further portion of CO is fed in.

The ethylenically unsaturated compounds used as reactant in the processaccording to the invention contain one or more carbon-carbon doublebonds. These compounds are also referred to hereinafter as olefins forsimplification. The double bonds may be terminal or internal.

The ethylenically unsaturated compounds may, in addition to the one ormore double bonds, contain further functional groups. At the same time,the ethylenically unsaturated compound preferably comprises a total of 2to 30 carbon atoms, preferably 2 to 22 carbon atoms, more preferably 2to 12 carbon atoms.

In one variant of the process, the ethylenically unsaturated compounddoes not comprise any further functional groups apart from carbon-carbondouble bonds.

In one variant of the process, the ethylenically unsaturated compound isselected from: ethene, propene, 1-butene, cis- and/or trans-2-butene,isobutene, 1,3-butadiene, 1-pentene, cis- and/or trans-2-pentene,2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, hexene,tetramethylethylene, heptene, 1-octene, 2-octene, di-n-butene, ormixtures thereof.

In one variant of the process, the ethylenically unsaturated compound isselected from: propene, 1-butene, cis-2-butene, trans-2-butene, ormixtures thereof.

In one variant of the process, the ethylenically unsaturated compound isselected from: 1-pentene, cis-2-pentene, trans-2-pentene,2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, or mixturesthereof.

Suitable mixtures of ethylenically unsaturated compounds are thosecalled raffinates I to III. Raffinate I comprises 40% to 50% isobutene,20% to 30% 1-butene, 10% to 20% cis- and trans-2-butene, up to 1%1,3-butadiene and 10% to 20% n-butane and isobutane. Raffinate II is aportion of the C₄ fraction which arises in naphtha cracking and consistsessentially of the isomeric n-butenes, isobutane and n-butane afterremoval of isobutene from raffinate I. Raffinate III is a portion of theC₄ fraction which arises in naphtha cracking and consists essentially ofthe isomeric n-butenes and n-butane.

In one variant, a mixture comprising isobutene, 1-butene, cis- andtrans-2-butene is used. Preferably, the mixture comprises 1-butene, cis-and trans-2-butene.

In one variant of the process, the alcohol in process step c) isselected from: methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol,1-hexanol, 2-propanol, tert-butanol, 3-pentanol, cyclohexanol, phenol.

In one variant of the process, the alcohol in process step c) ismethanol.

In one variant of the process, the substance comprising Pt is selectedfrom: platinum dichloride

(PtCl₂), platinum(II) acetylacetonate [Pt(acac)_(2]), platinum(II)acetate [Pt(OAc)₂], dichloro(1,5-cyclooctadiene)platinum(II)[Pt(cod)₂Cl₂], bis(dibenzylideneacetone)platinum [Pt(dba)₂],bis(acetonitrile)dichloroplatinum(II) [Pt(CH₃CN)₂Cl₂],(cinnamyl)platinum dichloride [Pt(cinnamyl)Cl₂].

In one variant of the process, the substance comprising Pt is selectedfrom: platinum dichloride (PtCl₂), platinum(II) acetylacetonate[Pt(acac)₂], platinum(II) acetate [Pt(OAc)₂].

CO is fed in in step d) preferably at a partial CO pressure between 0.1and 10 MPa (1 to 100 bar), preferably between 1 and 8 MPa (10 to 80bar), more preferably between 2 and 6 MPa (20 to 60 bar).

The reaction mixture is heated in step e) of the process according tothe invention preferably to a temperature in the range from 60° C. to160° C., preferably in the range from 80 to 140° C., more preferably inthe range from 100 to 140° C., in order to convert the ethylenicallyunsaturated compound to an ester.

The invention is to be illustrated in detail hereinafter by a workingexample.

Conversion of 1-Octene to the Methyl Ester

Reaction conditions: 1-Octene (1.0 mmol), PtCl₂ (0.01 mmol, 1.0 mol %),ligand: monodentate phosphine ligand (0.04 mmol, 4.0 mol %), bidentatephosphine ligand (0.02 mmol, 2.0 mol %), PTSAH₂O (monohydrate ofp-toluenesulfonic acid) (5.0 mol %), MeOH (2.0 ml), pressure (CO): 40bar, temperature: 120° C., reaction time: 20 h.

The reaction was conducted with the following ligands:

Monodentate Phosphine:

Bidentate Phosphine Ligands:

The respective yield and n/iso selectivity are stated below the ligand.Selectivities and yields were determined by gas chromatography withmesitylene as internal standard.

Of the 16 ligands used, 11 did not give any conversion (0%). Only withone ligand (L12=(1)) was it possible to achieve a conversion of morethan 60%. As shown by the series experiments, the greatest conversion isachieved with the inventive complex of Pt and (1).

The cost of Pt is below that of Pd. The object is thus achieved by acomplex according to the invention.

1-7. (canceled)
 8. Process comprising the process steps of: a) initiallycharging an ethylenically unsaturated compound; b) adding a complexcomprising Pt and a compound of formula (I)

or adding a compound having formula (I)

where R¹ R², R³, R⁴ are each independently selected from—(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, —(C₆-C₂₀)-heteroaryl; at least one of the R¹, R², R³, R⁴radicals is a —(C₆-C₂₀)-heteroaryl radical having at least six ringatoms; and R¹ R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl or—(C₆-C₂₀)-heteroaryl, may each independently be substituted by one ormore substituents selected from: —(C₁-C₁₂)-alkyl, —O—(C₁-C₁₂)-alkyl,—OH, —NH₂, halogen, and a substance comprising Pt; c) adding an alcohol;d) feeding in CO; e) heating the reaction mixture from a) to d), withconversion of the ethylenically unsaturated compound to an ester. 9.Process according to claim 8, wherein the ethylenically unsaturatedcompound is selected from: ethene, propene, 1-butene, cis- and/ortrans-2-butene, isobutene, 1,3-butadiene, 1-pentene, cis- and/ortrans-2-pentene, 2-methyl- 1-butene, 3-methyl- 1-butene,2-methyl-2-butene, hexene, tetramethylethylene, heptene, 1-octene,2-octene, di-n-butene, or mixtures thereof.
 10. Process according toclaim 8, wherein the alcohol in process step c) is selected from:methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol,2-propanol, tent-butanol, 3-pentanol, cyclohexanol, phenol.
 11. Processaccording to claim 8, wherein the alcohol in process step c) ismethanol.
 12. Process according to claim 8, wherein the substancecomprising Pt is selected from: platinum dichloride (PtCl₂),platinum(II) acetylacetonate [Pt(acac)₂], platinum(II) acetate[Pt(OAc)₂], dichloro(1,5-cyclooctadiene)platinum(II) [Pt(cod)₂Cl_(2],)bis(dibenzylideneacetone)platinum [Pt(dba)₂],bis(acetonitrile)dichloroplatinum(II) [Pt(CH₃CN)₂Cl₂],(cinnamyl)platinum dichloride [Pt(cinnamyl)Cl₂].
 13. Process accordingto claim 8, wherein the substance comprising Pt is selected from:platinum dichloride (PtCl₂), platinum(II) acetylacetonate [Pt(acac)₂],platinum(II) acetate [Pt(OAc)₂].